1. Field of the Invention
This invention relates to fluid driven dental handpieces, particularly of the straight type.
2. Description of the Prior Art
Modern dental handpieces of the above type generally comprise a chuck which is powered by an air driven motor located in the handpiece itself. Turbine motors are not generally satisfactory for straight type handpieces since they operate most efficiently at high speeds, on the order of 250,000 rpm or more and have relatively low torque. The speed of the turbine can be reduced by throttling the supply of air applied thereto under pressure, but in doing so, the torque is further reduced.
For certain types of dental work, it is often desirable to operate the handpiece at a relatively lower speed and at higher torque. For example, it is found that certain tooth cleaning, drilling and other operations are best performed at speeds on the order of 5,000 rpm whereas certain polishing operations are better performed at somewhat higher speeds, on the order of 15,000 to 25,000 rpm.
In our aforementioned patent application Ser. No. 477,803, we describe and claim a dental handpiece comprising two telescoping barrels, one carrying a vane type motor and the other carrying a chuck. A two speed transmission is provided to transmit rotation from the motor to the chuck and the barrels are movable axially relative to each other to shift the transmission from one speed setting to the other. This works quite satisfactory.
Such dental handpieces are very compact and must be easy and convenient for a dentist to manipulate. This imposes severe design problems since projecting controls for opening and closing the chuck, changing speeds, reversing direction of rotation, etc., must be kept to a minimum and must not interfere with proper operation of the handpiece or convenience in handling the same. Also, it is highly desirable for the barrels to normally freely swivel relative to each other so that the flexible power conduit, such as an air hose, for supplying power to the handpiece does not hinder manipulation of the part or barrel of the handpiece which is normally held by the dentist. Further, such handpieces must provide for ready attachment of the usual contra-angle tips or other tools thereto.
Although the handpiece of our above noted patent application Ser. No. 477,803 provided for the attachment of such contra-angle tips, the chuck moved axially a small amount relative to the forward barrel during opening and closing of the chuck and this tended to make it difficult to properly attach certain contra-angle tips thereto.